1. Field of the Invention
The present invention relates to an electronic distance meter having a sighting telescope.
2. Description of the Related Art
When a surveyor measures the distance between two points, an electronic distance meter (EDM) is generally used. An electronic distance meter calculates the distance via the phase difference between a projecting light and a reflected light and via the initial phase of an internal reference light, or via the time difference between the projecting light and the reflected light.
A typical electronic distance meter is provided, behind the objective lens of a sighting telescope thereof, with a light transmitting mirror positioned on the optical axis of the sighting telescope to project the measuring light toward a target through the center of the entrance pupil of the objective lens of the sighting telescope. The light which is reflected by the target to be passed through the objective lens of the sighting telescope passes the peripheral space of the light transmitting mirror to be captured via a wavelength selection filter and a light receiving mirror.
In such an electronic distance meter, the light which is reflected by the target and passed through the objective lens of the sighting telescope is interrupted by the aforementioned light transmitting mirror by a greater amount as the target is closer to the electronic distance meter. If the light which is reflected by the target and passed through the objective lens of the sighting telescope is interrupted by the light transmitting mirror by a great amount, the light amount of the incident light upon a light receiving element (photo-receiver) provided in the electronic distance meter decreases, which deteriorates the precision in measuring the object distance. If the target is very close to the electronic distance meter, the light which is reflected by the target and passed through the objective lens of the sighting telescope may not be incident on the light receiving element (photo-receiver) at all, which makes it impossible to perform a distance measuring operation. To prevent these problems from occurring, various methods have been proposed.
The present invention has been devised in view of the problems noted above, and accordingly, an object of the present invention is to provide an electronic distance meter which is free from the aforementioned problem of a decrease in the amount of incident light upon the aforementioned light receiving element when the target is close to the electronic distance meter, and furthermore, is free from the aforementioned problem of deterioration of the precision in measuring the object distance that is caused by a decrease in the amount of incident light upon the light receiving mirror. Another object of the present invention is to provide an electronic distance meter equipped with an autofocus system which is free from the above-mentioned problems.
To achieve the objects mentioned above, according to an aspect of the present invention, an electronic distance meter is provided, including a sighting telescope having an objective lens for sighting an object; a reflection member provided behind the objective lens, wherein the reflection member is positioned so as to be eccentric with respect to an optical axis of the objective lens; an optical distance meter which includes a light-transmitting optical system for transmitting a measuring light via the reflection member and the objective lens, and a light-receiving optical system for receiving a portion of the measuring light which is reflected by the object, subsequently passed through the objective lens, and not obstructed by the reflection member; and a measuring-light incident position changing device for changing an incident point of a central axis of the measuring light on a reflection surface of the reflection member between a first incident point on the reflection surface away from a point of intersection of the reflection surface and the optical axis of the objective lens, and a second incident point on the reflection surface on either the point of intersection or substantially on the point of intersection.
Preferably, the reflection member is positioned so as to satisfy the following relationship: b greater than c
wherein xe2x80x9cbxe2x80x9d designates the distance from the optical axis of the objective lens to an edge of a cross section of the measuring light in a first direction of eccentricity of the reflection member, and xe2x80x9ccxe2x80x9d designates the distance from the optical axis of the objective lens to an edge of the light reflection member in a second direction opposite to the first direction of eccentricity of the reflection member.
In an embodiment, the measuring-light incident position changing device includes a diaphragm positioned on an optical path of the measuring light. The incident point of a central axis of the measuring light on the reflection surface is changed by moving the diaphragm in a direction perpendicular to the optical path of the measuring light.
In an embodiment, the electronic distance meter further includes a controller which controls the measuring-light incident position changing device so that the measuring-light incident position changing device changes the incident point of the central axis of the measuring light to the first incident point and the second incident point when the object is positioned at a short distance and a long distance, respectively.
In an embodiment, the sighting telescope includes a focus adjustment lens guided along an optical axis of the sighting telescope; wherein the electronic distance meter further includes a lens position detection device which detects an axial position of the focus adjustment lens. The controller controls the measuring-light incident position changing device so that the measuring-light incident position changing device changes the incident point of the central axis of the measuring light between the first incident point and the second incident point in accordance with a result of detection of the lens position detection device.
In an embodiment, the measuring-light incident position changing device includes a plane-parallel plate disposed between a light-emitting element which emits the measuring light and the reflection member, wherein the plane-parallel plate is inclined with respect to a plane perpendicular to an optical axis of the light-transmitting optical system.
In an embodiment, the controller controls the plane-parallel plate so as to rotate in first and second rotational directions by a same angle of rotation when the object is positioned at the short distance and the long distance, respectively.
In an embodiment, the reflection member is made of a parallel-plate mirror having front and rear surfaces parallel to each other; wherein the reflection member is inclined to the optical axis of the objective lens. The surface of the reflection member on which the point of intersection is positioned is the front surface of the reflection member which faces the objective lens.
In an embodiment, the light-transmitting optical system includes a collimating lens positioned between the light-emitting element and the plane-parallel plate.
In an embodiment, the light-receiving optical system includes a wavelength selection filter positioned behind the reflection member.
In an embodiment, the measuring-light incident position changing device includes a motor for rotating the plane-parallel plate.
In an embodiment, the measuring-light incident position changing device includes two mirrors which are arranged parallel to each other and are provided between a light-emitting element which emits the measuring light and the reflection member, wherein one of the two mirrors is driven to move relative to the other of the two mirrors in order to change the incident position of the central axis of the measuring light.
According to an another aspect of the present invention, an electronic distance meter is provided, including a sighting telescope having an objective lens and a focusing lens for sighting an object; a reflection member provided behind the objective lens, wherein the reflection member is position so as to be eccentric with respect to an optical axis of the objective lens; an optical distance meter which includes a light-transmitting optical system for transmitting a measuring light via the reflection member and the objective lens, and a light-receiving optical system for receiving a portion of the measuring light which is reflected by the object, subsequently passed through the objective lens and not obstructed by the reflection member; a focus detecting device for detecting a focus state of the sighting telescope; and an autofocus drive system which drives the focusing lens to bring the object into focus in accordance with the focus state detected by the focus detecting device.
In an embodiment, the measuring light projected toward the object via the light-transmitting optical system travels toward the object along an optical path which is eccentric with respect to the optical axis of the objective lens.
In an embodiment, the electronic distance meter further includes a diaphragm positioned on an optical path of the measuring light. The measuring light is made to be eccentric with respect to the optical axis of the objective lens by moving the diaphragm in a direction perpendicular to the optical path of the measuring light.
In an embodiment, the reflection member is made of a parallel-plate mirror having front and rear surfaces parallel to each other, wherein the reflection member is inclined to the optical axis of the objective lens. A reflection surface of the reflection member on which a point of intersection of the reflection surface and the optical axis of the objective lens is positioned includes the front surface of the reflection member which faces the objective lens.
In an embodiment, the light-transmitting optical system includes a collimating lens positioned between the light-emitting element and the plane-parallel plate.
In an embodiment, the light-receiving optical system includes a wavelength selection filter positioned behind the reflection member.
In an embodiment, the electronic distance meter further includes a measuring-light incident position changing device for changing an incident point of the central axis of the measuring light on a reflection surface of the reflection member between a first incident point on the reflection surface away from the optical axis of the objective lens and a second incident point on the reflection surface on either the optical axis of the objective lens or substantially on the optical axis.
In an embodiment, the measuring-light incident position changing device includes a motor for rotating the plane-parallel plate.
In an embodiment, the measuring-light incident position changing device includes two mirrors which are arranged parallel to each other and are provided between a light-emitting element which emits the measuring light and the reflection member, wherein one of the two mirrors is driven to move relative to the other of the two mirrors in order to change the incident position of the central axis of the measuring light.
In an embodiment, the electronic distance meter includes a controller which controls the measuring-light incident position changing device so that the measuring-light incident position changing device changes the incident point of the central axis of the measuring light to the first incident point and the second incident point when the controller determines that the object is positioned at a short distance and a long distance, respectively, in accordance with the focus state of the sighting telescope which is detected by the focus detecting device.
In an alternative embodiment, the electronic distance meter includes a controller which controls the measuring-light incident position changing device so that the measuring-light incident position changing device changes the incident point of the central axis of the measuring light to the first incident point and the second incident point when the controller determines that the object is positioned at a short distance and a long distance, respectively, in accordance with an axial position of the focusing lens driven by the autofocus drive system.
In an embodiment, the measuring-light incident position changing device includes a plane-parallel plate disposed between a light-emitting element which emits the measuring light and the reflection member, wherein the plane-parallel plate is inclined with respect to a plane perpendicular to an optical axis of the light-transmitting optical system.
In an embodiment, the controller controls the plane-parallel plate so as to rotate in first and second rotational directions by a same angle of rotation when the object is positioned at the short distance and the long distance, respectively.
In an embodiment, the focus detecting device includes a phase-difference detection focus detecting device which detects an in-focus state from a correlation between a pair of images respectively formed by two light bundles which are respectively passed through two different pupil areas on the objective lens of the sighting telescope.
In an embodiment, the focus detecting device includes a phase-difference detection focus detecting device which detects an in-focus state from a correlation between a pair of images respectively formed by two light bundles which are respectively passed through two different pupil areas on the objective lens of the sighting telescope; wherein a direction of eccentricity of the reflection member extends perpendicular to a direction of separation of the two pupil areas.
The present disclosure relates to subject matter contained in Japanese Patent Application No.2000-154255 (filed on May 25, 2000) which is expressly incorporated herein by reference in its entirety.